1. Field of the Invention
The present invention relates to electrical connectors for connecting flexible boards to circuit boards.
2. Description of the Related Art
Japanese patent application Kokoku No. 3-051,257 discloses a so-called forceless connector for connecting a flexible board to a circuit board such as shown FIGS. 1 and 2. The connector includes a housing 51 having an opening at the upper right-hand corner. A pressure member 52 is attached to the housing 51 for rotation to cover the opening. The pressure member 52 is rotatable clockwise to a closed position as shown in FIG. 2 such that the front concave surface 53 of the pressure member 52 slides on the convex surface 54 of the housing 51. When the pressure member 52 rotates to the closed position, a latch claw 56 engages a latch shoulder 57 of the housing 51 to hold the pressure member in the closed position.
A number of contact elements 55 are arranged within the housing 51 in the direction perpendicular to the paper sheet. A contact portion 58 of each contact member 55 is bent in a U-shaped form so as to provide a spring property and has a front end extending diagonally upwardly toward the pressure member 52. A connection portion 59 is bent in an L-shaped form so as to extend downwardly through the housing 51 and an aperture P1 of a circuit board P.
In operation, the pressure member 52 is turned to the open position, and a flexible board F is inserted into the connector such that it slides on the lower surface of the pressure member 52 as shown in FIG. 1. Then, the pressure member 52 is turned clockwise to the closed position as shown in FIG. 2. Consequently, the pressure member 52 presses the flexible board F against the front ends 58 of the contact elements 55 so that the circuit conductors on the lower side of the flexible board F are brought into contact with the corresponding contact elements 55 while the latch claw 56 engages the latch shoulder 57 to hold the connection between the flexible board F and the contact elements 55.
In the above connector, however, the thickness of the pressure member 52 between the center of rotation of the pressure member 52 and the front ends 58A contact elements 55 increases toward the outside of the connector so that the pressure member 52 can open if the engagement between the latch claw 56 and the latch shoulder 57 is incomplete.
In order to prevent such a problem, the latch claw and shoulder must be sufficiently large to ensure the engagement. Such large latch claw and shoulder provided on the side of the connector make the connector itself larger.
Japanese patent application Kokoku No. 4-33671 discloses another forceless-type electrical connector such as shown in FIGS. 3 and 4. A housing 61 has an opening on the upper left corner. A pressure member 62 is supported by the housing 61 for rotation about the axis 63. A cylindrical portion 64 of the pressure member 62 engages a concave surface 65 of the housing 61 in sliding relation and is rotatable clockwise to the closed position as shown in FIG. 4.
A number of contact elements 66 are disposed within the housing 61 in the direction perpendicular to the paper. An contact portion 67 of each contact element 66 is bent in the U-shaped form so as to provide a spring property, with its tip facing toward the pressure member 62. A connection portion 68 extends downwardly through the housing 61 to be inserted into an aperture of a circuit board (not shown).
The pressure member 62 has two flat surfaces 69 and 70 connected to each other at a certain angle. When the pressure member 62 is turned to the closed position in FIG. 4, the upper flat surface 70 comes into contact with the flexible board F. The distance d1 between the axis 63 and the lower flat surface 69 is made less than the distance d2 between the axis 63 and the upper flat surface 70.
In operation, the pressure member 62 is turned counterclockwise to the open position, and a flexible board F is inserted into a space between the pressure member 62 and the contact portions 67 of contact elements 66 as shown in FIG. 3. Then, the pressure member 62 is turned clockwise to the closed position so that the upper flat surface 70 presses the flexible board F against the contact portions 67 of the contact elements 66 to thereby bring the electrical circuit of the flexible board F into contact with the contact elements 66 as shown in FIG. 4. The tips of the contact elements 66 contacting the flexible board F are located below the axis 63 so that the tips exert a reactive force on the pressure member 62 via the flexible board F tending to turn the pressure member 62 clockwise. Consequently, once turned to the closed position, the pressure member 62 is hardly opened, thus holding the flexible board F reliably.
However, the flexible board F contacts the contact elements 66 at a point as shown in FIG. 4 so that when the pressure member 62 is being opening, the flexible board F contacts the pressure member 62 at an edge formed by the adjoining upper and lower flat surfaces 69 and 70. Consequently, in order to hold the flexible board in proper contact with the contact elements 66, it is necessary that the contact points and edge be close in the insertion direction of the flexible board.
The aforementioned distances d1 and d2 depend on the thickness of the flexible board F. In order to assure proper insertion of the flexible board regardless of the thickness, it is necessary to keep the difference of the distances d2 and d1, or (d2-d1), constant, while in order to make the connector compact, it is necessary to reduce the distance d2. If the distance d2 is made very small, however, the distance d1 becomes too small to provide sufficient strength. As the difference (d2-d1) is made small while keeping the constant value, the edge between the flat surfaces 69 and 70 becomes so close to the axis 63 that the moment of a force on the pressure member 62 becomes too small to hold the pressure member 62. Other words, it is very difficult to produce a satisfactory moment in the clockwise direction for the pressure member 62 because of the limited shape, size, and tolerance of contact elements and the pressure member, thus failing to provide proper contact between the connector and the flexible board F. Especially, the contact elements are made by deforming metal pins, thus producing many shaping errors having adverse effects.
In addition, the middle portion of the pressure member which is supported by the housing at opposite ends for rotation tends to be bent upwardly by a force from the bottom, thus changing the contact pressure. This problem becomes worse as the number of contact elements increases.
Japanese UM patent application Kokai No. 4-61,883 discloses a still another conventional forceless electrical connector such as shown in FIGS. 5-7. An elongated substantially rectangular housing 71 has an opening on the upper left corner. A pressure member 72 is attached to the housing 71 for rotation about shaft portions 73 extending in the longitudinal direction of the housing 71. A cylindrical sliding surface 74 is formed on the pressure member 72 so as to slide on a guiding surface 75 of the opening so that the pressure member 72 is rotatable about the axis 76 between two positions as shown in FIGS. 6 and 7.
A number of contact elements 77 are arranged in the housing 71 in the longitudinal direction of the housing 71. A spring contact portion 78 has a U-shaped form and has a front portion facing the pressure member 72. A connection portion 79 extends downwardly through the housing 71 and then to the right side to be inserted into an aperture of a circuit board (not shown).
A pair of flat surfaces 40 and 41 are provided on the pressure member 72 and connected to each other at an angle. When the pressure member 72 is turned from the open position in FIG. 6 to the closed position in FIG. 7, the upper flat surface 41 is brought into contact with the flexible board F. The distance d3 between the upper flat surface 41 from the axis 76 is made larger than the distance d4 between the lower flat surface 80 and the axis 76.
In operation, the pressure member 72 is turned counterclockwise about the axis 76 to the open position, and a flexible board F is inserted into a space between the pressure member 72 and the contact portions 78 of contact elements 77 as shown in FIG. 6. The pressure member 72 is then turned clockwise to the closed position so that the upper flat surface 41 presses the flexible board F to the right as shown in FIG. 7. Consequently, the flexible board F is pressed against the contact portions 78 of contact elements 77 so that the circuit conductors of the flexible board F are brought into contact with the contact elements 77.
When the pressure member 72 is turned counterclockwise to the open position, it abuts against a shoulder 82 of the housing 71 so that the rotation of the pressure member 72 beyond the shoulder 82 are prevented. The torque applied to the pressure member 72 is proportional to the arm length L from the shoulder 42. The arm length L is generally set greater than the distance T between the shoulder 42 and the axis 76, so that the torque applied to the pressure member 72 becomes large.
As a result, the shaft portions 73 of pressure member 72 or the bearing portions of housing 71 can be broken, and the pressure member 72 comes off from the housing 71. The smaller the connector, the higher the frequency with which such accident occurs.